1. Technical Field
The present invention relates generally to multi-gap rotating electric machines for use in, for example, motor vehicles. More particularly, the invention relates to a multi-gap rotating electric machine which is suitable for use as a high-performance and small-sized electric motor in a hybrid vehicle.
2. Description of Related Art
Japanese Unexamined Patent Application Publication No. 2012-80692, an English equivalent of which is US Patent Application Publication No. 2012/0080977 A1, discloses a multi-gap rotating electric machine.
The multi-gap rotating electric machine includes a rotor and a stator. The rotor has an annular rotor core connected to a rotating shaft. The stator includes a stator core and a stator coil. The stator core includes an outer core part, an inner core part and a side core part. The outer core part has an annular shape and is located radially outside of the rotor core with a radially outer magnetic gap formed between the outer core part and the rotor core. The outer core part has a plurality of slots that are formed in a radially inner surface of the outer core part and spaced from one another in the circumferential direction of the outer core part. The inner core part has an annular shape and is located radially inside of the rotor core with a radially inner magnetic gap formed between the inner core part and the rotor core. The inner core part has a plurality of slots that are formed in a radially outer surface of the inner core part and spaced from one another in the circumferential direction of the inner core part. The side core part radially extends to connect the outer and inner core parts. The side core part is located on one axial side of the rotor core with an axial magnetic gap formed between the side core part and the rotor core. The side core part has a plurality of slots each of which is formed in an axial end face of the side core part facing the rotor core so as to communicate with one corresponding pair of the slots of the outer and inner core parts. The stator coil is formed of a plurality of electric wires mounted on the stator core. Each of the electric wires has a plurality of outer in-slot portions, a plurality of inner in-slot portions and a plurality of intermediate in-slot portions. Each of the outer in-slot portions is received in a corresponding one of the slots of the outer core part of the stator core. Each of the inner in-slot portions is received in a corresponding one of the slots of the inner core part of the stator core. Each of the intermediate in-slot portions is received in a corresponding one of the slots of the side core part of the stator core.
With the above configuration, the rotor core and the stator core face each other through the three magnetic gaps formed therebetween, i.e., the radially outer magnetic gap, the radially inner magnetic gap and the axial magnetic gap. Consequently, compared to the case of a rotating electric machine which has only a radially outer magnetic gap and a radially inner magnetic gap formed between the rotator core and the stator core, it is possible to increase the amount of magnetic flux transferred between the rotor and the stator, thereby increasing the output torque of the rotating electric machine.
Moreover, according to the disclosure of the above patent document, in assembling the stator, the electric wires are first assembled together to form the stator coil which has the shape of a ring. Then, the stator coil is axially moved toward the stator core from the opposite side to the side core part of the stator core, until the outer, inner and intermediate in-slot portions of the electric wires forming the stator coil are respectively inserted in the slots of the outer, inner and side core parts of the stator core.
However, to assemble the stator in the above manner, it is necessary to configure the slots of the outer and inner core parts of the stator core as open slots. More specifically, to allow the outer, inner and intermediate in-slot portions of the electric wires to be respectively inserted into the slots of the outer, inner and side core parts of the stator core from the opposite side to the side core part of the stator core, it is necessary to configure the slots of the outer core part to be fully open at the radially inner surface of the outer core part and the slots of the inner core part to be fully open at the radially outer surface of the inner core part. Further, with the open slots of the outer and inner core parts of the stator core, to suppress torque ripple, it is necessary to set the numbers of the slots of the outer, inner and side core parts of the stator core to be twice or more larger than usual. Consequently, with the increased numbers of the slots, the manufacture of the stator is complicated, thereby increasing the manufacturing cost.